The invention relates to an expansion joint reinforcing structure for concrete slabs, comprising a first profile element to be attached to an edge of a first concrete slab, and a second profile element to be attached to an edge of a second, adjacent, concrete slab, said profile elements being joined together by at least one removable connecting strip such that there is a gap between the profile elements.
A widely used flooring structure in construction engineering is a concrete slab on grade, poured either direct on top of leveled soil or on top of a thermal insulator layer placed on the ground. Shrinkage of the concrete as well as thermal contraction and expansion tend to cause cracking in large slabs, whereby large slabs have to be divided into smaller sub-slabs by means of expansion or isolation joints. Deformations caused by shrinkage and thermal expansion and contraction will thus occur at the expansion joints and the slabs will otherwise remain crackless.
The simplest way of making expansion joints is to first pour a whole concrete slab and then, as setting has begun, divide it into smaller sections separated by grooves saw-cut on the surface of the slab by means of a diamond-blade saw. Subsequent contraction cracks will then appear at the grooves. The edges of saw-cut expansion joints are prone to crumbling and chipping, so they are totally unsuitable for heavily loaded floors. From the prior art we also know of expansion joint structures embedded in concrete with metal reinforcements at the edges of the expansion joints. One such structure is disclosed in the patent document FI 952994. The reinforcing joint structure is embedded in fresh concrete, and the joint between the flat steel bars is saw-cut open once the concrete has hardened. The joint is then filled with elastic material. The installation of such an expansion joint structure is tedious, because the joint structure has to be pushed into already-leveled fresh concrete. Moreover, saw-cutting the expansion joint means extra work.
Reference documents GB 1139538, U.S. Pat. No. 3,068,763, U.S. Pat. No. 3,276,335, and U.S. Pat. No. 3,455,215 disclose expansion joint structures embedded in the surface of a concrete slab. These structures are weak and not intended to be anchored in the concreting base. Therefore, they cannot serve as construction joint forms or screed guides during the floating of the concrete slab. In most such solutions, the gap between the two halves of the joint structure is closed using a flexible sealing agent attached to the joint structure and remaining partly within the cast. Such a flexible and soft sealing agent wears and breaks easily so that the joint begins to leak. Moreover, the sealing agent within the cast cannot be replaced.
Patent document FI 982675 discloses an expansion joint structure with a sheetmetal profile and metallic angle profile loosely attached to the sheetmetal profile by rivets or flexible bolts, for example. The sheetmetal profile simultaneously serves as a form for the slab to be cast. The sheetmetal profile and angle profile both have protruding bondage means through which they become attached to the concrete. The joint structure is placed such that it rests on corrugated steel rods driven into the concreting base at correct locations and heights, or on concrete legs cast on the concreting base, after which the slab is poured. As the concrete shrinks, the angle profile comes off the sheetmetal profile, thereby opening an expansion joint between the profiles.
A drawback of this solution is the poor functionality of the expansion joint. An expansion joint caused solely by the shrinkage of concrete is so narrow that it cannot be sealed with a sealing agent. This means that the expansion joint will not be watertight. In order to achieve a sufficient joint width the gap between the sheetmetal profile and angle profile has to be enlarged with the result that the gap will be filled with concrete when the concrete is poured. Therefore, prior to sealant installation, the gap has to be thoroughly cleaned with e.g. a grinder, adding to the building costs. In spite of the cleaning, concrete dust and crumbles often remain in the gap, affecting the adhesion of the sealant to the walls of the gap. It is therefore difficult to male the expansion joint watertight. Moreover, it is somewhat difficult to anchor the expansion joint structure to the concreting base and set it at the correct height.